Alloy



Patented Jan. 7, 1936 UNITED STATES PATENT OFFICE ALLOY Roy E. Paine,Cleveland, Ohio, assignor to Magnesium Development Corporation, acorporation of Delaware No Drawing. Application October 4, 1933,

, Serial No. 692,133

2 Claims.

The invention relates to magnesium-base alloys and is directed to thedevelopment of alloys of this class which have good corrosionresistance, particularly in the cast and in the cast and hea treatedcondition.

The art of casting magnesium presents many practical difliculties whichmust be surmounted before the true commercial possibilities of magnesiumcastings can be fully realized. An alloy which is suitable for oneapplication may be entirely unsuited to another and, as a. consequence,it is frequently necessary to sacrifice desirable characteristics of thealloy in order to more fully realize the advantages of some one or moreimportant characteristics. Thus a compromise must quite frequently bemade in order to approach in one alloy the optimum properties for agiven application. For example, it may be found that corrosionresistance can be sacrificed to a certain extent to obtain highertensile strength, yield point, hardness, or similar mechanicalproperties. Again, tensile strength may be sacrificed in order to obtainproper casting or working characteristics. It is an object of thepresent invention to develop magnesium alloys which will combine to amaximum degree the characteristics of corrosion resistance, favorablemechanical properties, workability, susceptibility to improvement byheat treatment and adaptability to sand casting.

A further object is the provision of magnesium allo'ys characterized bytheir susceptibility to be improved in mechanical properties by suitablethermal treatments. A further object is the provision of magnesium-basealloys characterized by good corrosion resistance in either the cast orin the cast and heat treated condition. A further object is theprovision of magnesium alloys possessing excellent castingcharacteristics. A further object is the provision of magnesium-basealloys susceptible, within certain ranges, to mechanical deformation.

I have discovered that magnesium-base alloys containing from 0.5 percent to 22 per cent of lead possess to an appreciable degreethecollective characteristics of alloys whichare resistant to corrosion,alloys which may be readily cast, alloys which are susceptible toalteration of properties by thermal treatments, alloys having favorablemechanical properties, and alloys which, within a restricted range, maybe worked by extrusion, forging, orother means of mechanicaldeformation.

In accordance with my invention lead may be present in amounts as low as0.5 per cent. The preferred casting alloys are those containing aboveabout 5 per cent of lead since it is in these alloys that the mostpronounced combination of these different properties is obtained. Thealloy may be worked by extrusion over a range of from about 0.5 per centto about 22.0 per cent of- 6 lead. As an all around casting alloy I havefound a magnesium alloy containing 5 to 10 per cent of lead to beparticularly adapted to general foundry purposes. Alloys falling withinthis preferred range of composition as well as other alloys 10 comprisedwithin the broader limits previously defined, have been subjected tosevere tests designed to produce accelerated corrosion. Sand cast testbars poured in accordance with the best casting practice in the art weresubjected to cor- 15 rosion tests in the as cast and in the heat treatedcondition. In the example referred to the heat treatment was carried outat about 459 centigrade for about 20 hours followed by quenching inwater, and both heat treated and unheat 20 treated test bars weresubjected to that corrosion test which comprises alternately immersingthe metal in, and removing it from a 3 per cent sodium chloride solutionfor about hours, a treatment referred to hereinafter as the alternate 25immersion treatment.

There are certain elements 'which may be added to the binarymagnesium-lead alloys to particular advantage. Such, for instance, arethe metals calcium, cadmium and zinc. These may be, added singly or incombination with each other, the zinc in amounts between about 1.0 percent and 10.0 per cent, the calcium between about 0.1 per cent and 2.0per cent, and the cadmium between about 1.0 per cent and 10.0 per cent.35

' These alloying elements are substantial equivalents as indicated bytheir susceptibility to thermal treatment in magnesium-lead alloys. Thecalcium favorably affects the casting properties of the alloy withoutmarkedly decreasing its corrosion resistance. For instance, a magnesiumalloy containing 21.4 per cent of lead and 0.25 per cent of calciumshows, in the as cast condition, a strength loss of only 17 per centafter alternate immersion in a 3 per cent sodium chloride solu- 45 tionfor about 80 hours, while a heat treated magnesium alloy containingabout 5 per cent of lead to which about 0.25 per cent of calcium hadbeen added did not undergo any appreciable loss in strength under theforegoing corrosion conditions; the heat treatment in this case was atreatment at about 450 centigrade for about 20 hours. An alloy ofmagnesium with about 5.1 per cent of lead and 10.0 per cent of cadmiumhad in the sand cast condition a tensile 55 strength of about 24,650pounds per square inch and an elongation of about 9.8 per cent in 2inches. After a heat treatment of about 20 hours at about 450 centigradeits tensile strength had increased to about 25,140 pounds per squareinch and its elongation to 10.3 per cent in 2 inches. After an alternateimmersion corrosion test for hours the loss in strength was only 30 percent. A similarresult was obtained with a magnesiumbase alloy containingabout 5.3 per cent of lead and about 5.0 per cent of cadmium. An alloyof magnesium with about 5.0 per cent of lead and 5.0 per cent of zinchad in the sand cast condition a tensile strength of about 23,370 poundsper square inch. After a thermal treatment of about 20 hours at 450centigrade followed by an aging treatment of about 20 hours atcentigrade its strength had increased to about 25,710 pounds per squareinch. After an alternate immersion corrosion test of 80 hours the lossin strength was only 12 per cent. Another alloy of magnesium with about5.2 per cent of lead and 3.2 per cent of zinc under similar conditionslost only about 10 per cent after 80 hours alternate immersion in thecorrosive solution- As a preferred composition for alloys of this natureI advise (1) 5.0 per cent lead, 1.0 per cent calcium, balance magnesium;(2) 5.0 per cent lead, 5.0 per cent cadmium, balance magnesium; (3) 5.0per cent lead, 5.0 per cent zinc, balance magnesium. If more than one ofthe elements calcium, cadmium, or zinc be present simultaneously, Iprefer not to exceed a total of 10.0 per cent for these elements.

One of the disadvantages of the alloys described herein which may affecttheir use in certain applications, particularly where high strength is aleading or very material consideration, is the fact that the grainstructure of these alloys (with or without calcium) tends to be coarse.I have found that the metals aluminum and silicon form a class ofalloying elements which may be added to magnesium-lead alloys and aresubstantially equivalent in this respect that they materially refine thegrain structure of the alloy. Aluminum, for instance, can be added overa wide range, such as between 1.0 and 15.0 per cent; silicon may beeffectively present for this purpose in amounts of about 0.1 to 2.0 percent. When used in combination it is advisable that the total content ofaluminum and silicon does not exceed 15.0 per cent. In the preferredpractice of my invention I have found that the best results are usuallyobtained when the aluminum is present in amounts between 5 and 10 percent.

As a preferred magnesium-lead-silicon composition I use a magnesium-basealloy containing 7.0 per cent of lead and 0.5 per cent. of silicon. As apreferred magnesium-lead-aluminum alloy I use a magnesium-base alloycontaining 7.0 per cent of lead and 5.0 per cent of aluminum. When thealuminum and silicon are used in conjunction I prefer to use a total ofabout 5.0 per cent of aluminum and silicon combined, for instance about4.0 per cent aluminum and 1.0 per cent silicon.

Manganese alone may be added to magnesiumlead alloys in amounts between0.1 per cent and 1.0 per cent and has a stabilizing effect upon thealloy properties in that it raises the hardness slightly, does notmaterially decrease the corrosion resistance, and adds to the matrix ofthe alloy a hardening element which expresses itself not only in anincrease in tensile strength but also in surface hardness. An alloy ofthis nature containing about 8.0 per cent of lead and 0.85 per cent ofmanganese lost only 6 per cent of its original strength after 80 hoursalternate immersion in a 3 per cent aqueous solution of sodium chlorideand in the solution heat treated condition lost only 7 per cent of itsstrength in the alternate immersion treatment. A magnesium alloycontaining about 10.37 per cent of lead had lost only about 10 per centof its strength at the expiration of this period as compared withcertain other commercial alloys, such as, for instance, the well knownmagnesium alloy containing about 7 per cent of aluminum and 0.4 per centof manganese which, at the end of 40 hours of alternate immersion, hadlost about 60 per cent of its strength.

Very favorable alloys can be compounded by using as a base an alloy ofmagnesium, lead and aluminum and making additions thereto of at leastone of the class of metals tin, manganese or zinc. The lead can be usedin amounts from about 0.5 per cent to about 22.0 per cent, the aluminumfrom about 1.0 per cent to about 15.0 per cent, the tin from about 1.0per cent to about 15.0 per cent, the manganese from about 0.1 per centto about 1.0 per cent, and the zinc from about 1.0 per cent to about10.0 per cent. A sand cast alloy within this range had, in the as castcondition, a tensile strength of 27,500 pounds per square inch and anelongation of 5.7 per cent in 2 inches. After a thermal treatment of 16hours at 315 centigrade, the alloy had a tensile strength of 29,640pounds per square inch and an elongation of 6.0 per cent in 2 inches.Some of the heat treated specimens were then given an alternateimmersion treatment for 40 hours and after the treatment the specimenshad a tensile strength of 28,413 pounds per square inch and anelongation of 5.8 per cent in 2 inches, this alloy containing 5.0 percent of aluminum, 5.0 per cent of lead, 0.4 per cent of manganese and2.0 per cent of zinc. The loss in strength on the corrosion treatment isobserved to be less than 5 per cent as compared to about 60 per centwith the commercial magnesium-aluminum-manganese alloy disclosedhereinbefore which contains about 7' per cent of aluminum and 0.4 percent of manganese. As preferred compositions for alloys of this nature Iadvise (1) 7.0 per cent of lead, 7.0 per cent of aluminum, 2.0 per centtin, balance magnesium; (2) 7.0 per cent lead, 7.0 per cent aluminum,2.0 per cent tin, 0.5 per cent manganese, balance magnesium; (3) 7.0 percent lead, 7.0 per cent aluminum, 2.0 per cent tin, 2.0 per cent zinc,balance magnesium.

Two alloy compositions within this range which I have used to advantageare as follows: A magnesium-base alloy containing 8.0 per cent ofaluminum, 3.0 per cent of lead, 0.4 per cent of manganese, 1.0 per centof zinc, and 3.0 per cent of tin; a magnesium-base alloy containing 8.0per cent of aluminum, 1.0 per cent of lead, 0.4 per cent of manganese,1.0 per cent of zinc, and 1.0 per cent of tin.

The addition of lead to the magnesium-aluminum-manganese alloysincreases very considerably the corrosion resistance of these alloys,since with the addition of about 7 per cent of lead toan alloycontaining 7 per cent of aluminum and 1 per cent of manganese, the lossof strength after the alternate immersion test was only about 30 percent, as compared with about 60 per cent of the same alloy without lead.

Alloys of magnesium with lead, aluminum. and

manganese have been disclosed hereinabove. I have discovered that if toa base alloy of magnesium-lead-aluminum-manganese I add one or more ofthe class of metals calcium or cadmium, the resulting alloys becomeconsiderably more susceptible to variation of properties by thermaltreatments and their hardness can be markedly increased by artificialaging after thermal solution treatments. In'these alloys the leadcontent should range from about 0.5 per cent to about 22.0 per cent, thealuminum from about 1.0 per cent to about 15.0 per cent, and themanganese from about 0.1 per cent to about 1.0 per cent. To theseelements as a common base I add the elements calcium, or cadmium, singlyor in combination, the calcium in amounts from about 0.1 per cent toabout 2.0 per cent, the cadmium from about 1.0 per cent to about 10.0per cent. As an example of an alloy of this nature, a sand cast specimenof a magnesium-base alloy containing about 10.0 per cent of lead, about7.0 per cent of aluminum, about 0.4 per cent of manganese,

and about 5.0 per cent of cadmium, had in the cast condition a tensilestrength of about 23,200 pounds per square inch. After a thermalsolution treatment of 21 hours at about 430 centigrade the tensilestrength of the alloy had increased to about 36,000 pounds per squareinch, a gain in strength of about per cent. The same alloy after thesolution treatment had a Brinell hardness of about 61 and this hardnesswas raised to about 84 by an additional aging treatment of 20 hours atabout 175 centigrade, the tensile strength increasing slightly to about37,000 pounds per square inch.

Similarly a magnesium-base alloy containing about 5.0 per cent of lead,7.0 per cent of aluminum, 10.0 per cent of cadmium, and 0.4 per cent ofmanganese had in the sand cast condition a tensile strength of about24,000 pounds per square inch. After a thermal treatment of 21 hours atabout 430 centigrade the alloy had a tensile strength of about 35,000pounds per square inch. An additional aging treatment raised the Brinellhardness of the alloy from about 61 to about 79.

Similarly, a magnesium-base alloy containing about 5.0 per cent of lead,10.0 per cent of cadmium, 7.0 per cent of aluminum, 1.0 per cent ofmanganese, and 0.25 per cent of calcium had in the sand cast condition atensile strength of about 24,290 pounds per square inch. After a thermaltreatment of 20 hours at about 430 centigrade this alloy had a tensilestrength of about 33,200 pounds per square inch. After an additionalthermal treatment of about 20 hours at about 150 centigrade the strengthincreased to about 35,600 pounds per square inch and the Brinellhardness from about 47 to about 66.

Another magnesium-base alloy containing about 10.0'per cent of lead, 7.0per cent of aluminum, 5.0 per cent of cadmium, 0.4 per cent ofmanganese, and 0.1 per cent of calcium, had in t the sand cast conditiona tensile strength of about 23,210 pounds per square inch. After athermal solution treatment of 21 hours at about 430 cent grade the alloyhad a tensile strength of about 36,030 pounds per square inch; theBrinell hardness was about 61. After an additional aging treatment ofabout 20 hours at about 175 centigrade its tensile strength was about37,010 pounds per square inch and its Brinell hardness about 84. As adesirable alloy of this nature I advise 7.0 per cent lead, 7.0 per centaluminum and 0.4 per cent manganese. If more than one of the elementscalcium or cadmium are present simultaneously, the total should notexceed about 10.0 per cent for preferred purposes. 5

The addition of zinc in amounts from about 1.0 per cent to about 10.0per cent to magnesiumlead alloys containing aluminum and silicon incombination decreases the linear shrinkage, thus favorably aifecting thecasting properties, and 10 also increases the corrosion resistance andraises the yield point of these alloys. In alloys of this type the leadshould range from 0.5 per cent to 22.0 per cent, the aluminum from 1.0per cent to 15.0 per cent, and the silicon from 0.1 15 per cent to 2.0per cent, but the total amount of aluminum and silicon should preferablynot exceed 15.0 per cent.

A useful alloy of this nature is a magnesiumbase alloy containing about10.0 per cent lead, 8.0 20 per cent aluminum and 3.25 per cent zinc.Another useful composition is attained by substitutihg about 1.0 percent silicon for part or all of the aluminum.

An alloy similarly improved in casting proper- 25 ties, although not tosuch a decided extent, is one containing from about 0.5 per cent to 22.0per cent of lead, from about 1.0 per cent to about 10.0 per cent ofzinc, and from about 0.1 per cent to about 2.0 per cent of silicon. Afavorable alloy within this range is a magnesium-base'alloy consistingof about 10.0 per cent of lead, about 3.25 per cent of zinc, and about1.0 per cent of silicon, the balance being substantially magnesium.

V In making up alloys of the compositions dis-, closed hereinabove thealloys may be compounded by any of the methods known in the art. In'casting the alloys recourse may be had to the protective measuresdisclosed in existing pat- 40 ents and the published literature relatingto easily oxidizable metals. The alloys, especially themagnesium-leadbinary alloys, may be extruded over the entiredisclosed compositionrange. but other types of mechanical deforma- 46 tion such as rolling orforging should be carried on withdu'e regard for the fact that as thepercentage of total added alloying elements increases, the necessity forprecaution in working the alloy also increases.

It is my object to retain, as far as possible, the advantages of the useof magnesium base, such as low specific gravity, while securing inaddition the hereinabove disclosed benefits accruing from the additionsof the other alloying elements herein outlined. Accordingly, where inthe appended claims the term magnesium-base alloy is used, it refers toan alloy containing more than approximately 50 per cent of magnesium.

This application is a continuation in part of 50 my copendingapplication Serial No. 643,052,

I filed November 17, 1932.

- ROY E. PAINE.

